The present invention relates to an apparatus for supporting the magnetic heads in a two-sided floppy disk drive.
In a conventional support apparatus for the magnetic heads of a two-sided floppy disk drive, a first head is usually secured to a movable carriage and prevented from moving towards or away from the surface of the disk, while the second magnetic head is mounted on a rotatable arm to permit the second head to be moved towards or away from the surface of the disk. A conventonal magnetic read support apparatus of this type is illustrated in FIG. 1. A pair of read/write magnetic heads 4 and 5 are supported on a carriage 1 movable along an unillustrated guide rail in the radial direction with respect to a floppy disk 2. A first magnetic read/write head 4 is bonded to a base 3 rigidly secured to a front end of the carriage 1. A second magnetic read/write head 5 is positioned on the opposite side of the disk 2 so facing the first magnetic head 4 and is supported by the front portion of a rotatable arm 6. The arm 6 is supported by the rear portion of the carriage 1 through a flat spring 8, one end of which is secured to the rear portion of the arm 6 by insertion molding or other applicable means, and the other end of which is secured to the rear portion of the carriage 1 by a screw 15. The arm 6 has an tapered extension 6b which extends downwards towards the back surface of the secon magnetic head 5. The lower end of the tapered extension 6b contacts the back surface and acts as a pivot for the rotation of the second magnetic head 5. The second magnetic head 5 is bonded to the center of a gimbal spring 7 whose ends are secured to the front portion of the arm 6. A counterclockwise biasing force is applied to the arm 6 by a torsion spring 9 mounted on a sub-frame 10 and secured to the carriage 1 by the screw 15. The arm 6 has an L-shaped lever 6a formed on its top surface which engages with the bail 11 of an unillustrated solenoid.
In FIG. 1, the floppy disk 2 is shown mounted on a spindle 12 which rotates the disk 2. The disk 2 is held against the spindle 12 by a cap unit 13 which rotates with the spindle 12. The cap unit 13 has a shaft 14 projecting from its upper surface by which the cap unit 13 can be raised and lowered in the axial direction of the shaft 14. The spindle 12 has a cylindrical cavity 12a formed in its center into which the cap unit 13 is inserted, thereby clamping the disk 2 between the cap unit 13 and the spindle 12.
The force exerted on the disk 2 by the cap unit 13 when the disk 2 is held between the spindle 12 and the cap unit 13 produces wrinkles in the surface of the disk 2. While the spindle 12 is usually made of a metal such as aluminum or brass, the cap unit 13 is made of a softer material such as zircon or a polycarbonate. As a result, the wrinkles in the disk 2 are formed mainly in the top surface of the disk 2 which contacts the cap unit 13, as shown in FIG. 1. When the wrinkles pass between the magnetic heads, the second magnetic head 5 is vibrated up and down as it follows the surface of the disk 2.
When the slopes of the wrinkles in the surface of the disk 2 are gradual, the accelerations of the second magnetic head 5 in the direction normal to the surfaceof the disk 2 are small, and the second magnetic head 5 is able to follow the undulating surface of the disk 2. However, if the slopes of the wrinkles are steep, the second magnetic head 5 undergoes large accelerations in the normal direction, and the force required to keep it in contact with the surface of the disk 2 increases. However, the torsional spring 9 is designed to apply a constant force on the second magnetic head 5 of generally no more than 20 grams, which is insufficient when the second magnetic head 5 undergoes large accelerations. As a result, the second magnetic head 5 may be bounced away from the surface of the disk 2 by the accelerations.
Accordingly, the conventional apparatus illustrated in FIG. 1 has the problem that stable contact between the magnetic heads and the disk 2 can not be maintained, and the ability of the magnetic heads to read and write information is therefore decreased. Although the force applied on the second magnetic head 5 by the torsion spring 9 can be increased to prevent the second magnetic head 5 from bouncing off, this increases the wear on the disk 2 by the magnetic heads and reduces the lifespan of the disk 2.
Generally, the head core of the second magnetic head 5 is located closer to the radial center of the disk 2 than is the head core of the first magnetic head 4. As a result, the recording density of the disk 2 on the side facing the second manetic head 5 is higher than on the opposte side. However, since wrinkles are mainly formed on the side facing the second magnetic head 5, this side often has a higher error rate compared to the side facing the first magnetic head 4. Therefore, it is necessary to achieve stable contact between the disk 2 and the second magnetic head 5 to improve performance.
Another problem with the conventional apparatus illustrated in FIG. 1 is that the disk 2 can be damaged due to the so-called "tapping" taking place when the arm 6 which supports the second magnetic head 5 is raised or lowered. When the arm 6 is lowered by the force of the torsion spring 9, the second magnetic head 5 tends to collide with the disk 2. In addition, when the arm 6 is raised by an unillustrated solenoid to cause the second magnetic head 5 to separate from the disk 2, due to the gimbal spring 7 which supports the second magnetic head 5 having a small spring constant, the second magnetic head 5 may strike against the disk 2. In either case, the impact between the second magnetic head 5 and the disk 2 can damage the disk 2 and reduce its lifespan.